The invention relates to an acceleration or deceleration sensor comprising a housing which includes a plurality of mutually parallel tunnel-shaped cavities. A reed switch is disposed in at least one of the cavities and two rod-shaped permanent magnets are disposed end-to-end in at least one other cavity. The arrangement of the permanent magnets is such that two identical poles thereof face one another and at least one of the permanent magnets is displaceable in the longitudinal direction. The reed switch or switches are arranged in such a way that they are actuated by the magnetic field of the displaceable permanent magnet upon its displacement.
Sensors of the above-outlined type which, however, have but a single reed switch and a single tunnel-shaped cavity with a movable permanent magnet disposed therein are disclosed, for example, in German Patent No. 3,338,287, to which corresponds U.S. Pat. No. 4,639,563. They are employed, among others, in safety devices for automobiles. Such safety devices may comprise, for example, a bag that can be inflated by compressed air or other gas and is disposed in the region of the steering wheel. In case of a head-on collision, the bag is suddenly inflated and thus prevents the driver from hitting the steering wheel. The compressed air required to inflate the bag is on board in a compressed air bottle which is normally sealed by means of a magnetic valve. In case of a head-on collision, the magnetic valve opens and the path is released for the compressed air so that it is able to flow from the supply bottle into the air bag. The magnetic valve may be actuated (opened) by an acceleration and deceleration sensor to which the invention is directed. For this purpose, the sensor may directly switch a triggering system, such as a thyristor, or another appropriate electronic triggering circuit.
The acceleration and deceleration switch may find uses in other environments, such as centrifuges and the like.
Sensors of the described type are required in large quantities. It is desirable that the sensors themselves take up as little space as possible and that their response behavior fluctuate within narrow limits. It is furthermore expected that the response range, that is, the acceleration or deceleration at which the reed switch is closed can be set to meet the respective requirements and that the set value is adhered to as accurately as possible. These requirements are difficult to meet with the conventional structures. This drawback may be overcome, for example, by producing and testing a larger number of sensors, and selecting them according to the measuring results.